1. Field of the Invention
This invention relates to an objective lens driving device for driving and displacing an objective lens, converging and radiating an outgoing light beam from a light source, such as a semiconductor laser, to an optical recording medium, such as an optical disc or a magneto-optical disc, in a direction of an optical axis of the objective lens or in a planar direction perpendicular to the optical axis, by an electro-magnetic driving means, and a method for manufacture thereof. More particularly, it relates to an objective lens driving device in which a supporting member supporting the objective lens is used as a feeder line to a driving coil, and a method for manufacture thereof.
2. Description of the Related Art
A recording and/or reproducing apparatus, employing an optical recording medium, such as an optical disc or a magneto-optical disc, as a recording medium for recording information signals, includes an optical pickup unit for radiating a light beam onto a signal recording surface of an optical recording medium or detecting the return light reflected from the signal recording surface for recording or reading out information signals on or from the recording medium.
The optical pickup has a light source, such as a semiconductor laser, for radiating a light beam onto the signal recording surface of the optical recording medium, an objective lens for radiating and converging the light beam outgoing from the light source on the signal recording surface of the optical recording medium.
In addition, the optical pickup has an objective lens driving device for driving and displacing the objective lens, radiating and converging the light beam from the light source on the signal recording area of the optical recording medium, in a focusing direction along the optical axis of the lens and in a tracking direction along a plane perpendicular to the optical axis, for converging the light beam on the signal recording area and correctly tracing a recording track formed on the recording medium.
This sort of the objective lens driving device, shown in FIG. 1, includes four flexible linear supporting members 3, such as wires, supporting a lens holder 2 holding an objective lens 1 for supporting the objective lens 1 for movement in the focusing direction along the optical axis of the objective lens 1 as indicated by arrow F in FIG. 1 and in the tracking direction along the plane perpendicular to the optical axis as indicated by arrow T in FIG. 1. The objective lens driving device shown in FIG. 1 is so designed and constructed that the lens holder 2 is supported on the distal ends of the four supporting members 3 having their proximal ends supported in a cantilevered fashion on a stationary support substrate 5 set upright on a supporting base plate 4, formed of a magnetic metal plate and constituting a magnetic yoke. Thus the objective lens 1 held by the lens holder 2 is supported for movement in the focusing direction indicated by arrow F in FIG. 1 and in the tracking direction as indicated by arrow T in FIG. 1.
The objective lens driving device shown in FIG. 1 has an electro-magnetic driving unit for driving and displacing the lens holder 2 inclusive of the objective lens 1 in the focussing direction indicated by arrow F in FIG. 1 and in the tracking direction as indicated by arrow T in FIG. 1. The electro-magnetic driving unit is made up of a focusing driving coil 6 placed around the outer periphery of the lens holder 2, a pair of tracking driving coils 7 connected to the lateral side of the driving coil 6 and a magnetic circuit comprised of a pair of magnets 9, 9 mounted on a pair of upstanding pieces 8, 8 in turn mounted upright on the supporting base plate 4. The magnets 9, 9 are mounted on the upstanding pieces 8, 8 for facing the focusing driving coil 8 and the tracking driving coils 7.
On the supporting base plate 4 are mounted yoke pieces 8a, 8a facing the upstanding pieces 8, 8. These yoke pieces 8a, 8a are passed through through-holes 2a, 2a of the lens holder 2 for facing the magnets 9, 9.
The driving coil 6 for focussing and the driving coils 7 for tracking, making up the electro-magnetic driving unit, is fed with the control current corresponding to the focusing error signal and the tracking error signal produced on detecting the return light radiated via the objective lens 1 on the optical recording medium and reflected therefrom by a photodetector. If the control current is supplied to the driving coils 6 and 7 from a control circuit, a driving force is generated by the interaction of the magnetic flux of the magnets 9, 9 and the current flowing through the driving coils 6 and 7. Thus the lens holder 2 holding the objective lens 1 is displaced in the focusing direction indicated by arrow F and in the tracking indicated by arrow T in FIG. 1, at the same time as the four supporting members 3 are displaced flexibly.
For supplying the control currents corresponding to the focusing error signal and the tracking error signal to the driving coil 6 for focusing and the driving coils 7 for tracking, mounted on the lens holder 2, carrying the objective lens 1 and adapted for being displaced along with the objective lens 1, it is necessary to provide an electric connection between the driving coils and the control circuit as a supply source for the control currents.
Thus there is proposed such an objective lens driving device in which the supporting members 3 supporting the lens holder 2 are formed by electrically conductive linear metallic members and used as feeder lines for supplying the current to the driving coils 6 and 7. With this objective lens driving device, a printed wiring board 10 having an wiring pattern 10a formed thereon is mounted on an outer lateral surface of a stationary supporting substrate 5, and an electrical connection is established between the supporting members 3 and the control circuit, not shown, via the printed wiring board 10, as shown in FIG. 1. The driving coils 6, 7 have their coil ends 6a, 7a connected to distal ends 3a of the supporting members 3 protruded from supporting pieces 11 provided on the lateral side of the lens holder 2 for allowing the control currents to be supplied via the supporting members 3 to the respective driving coils 6 and 7.
Meanwhile, the connection between the driving coils 6, 7 and the supporting members 3 is established by placing the coil ends 6a, 7a around the distal ends 3a of the supporting members 3. If the electrical connection should be established in this manner by placing the coil ends 6a, 7a around the distal ends 3a of the supporting members 3, the assembling operation becomes complicated such that the objective lens driving device cannot be assembled efficiently. On the other hand, electrical connection cannot be established reliably by simply placing the coil ends 6a, 7a around the distal ends 3a of the supporting members 3.
For assuring reliable and efficient connection between the driving coils 6, 7 and the supporting members 3, it has been proposed to connect the coil ends 6a, 7a to the distal ends 3a of the supporting members 3 using a solder 12, as shown in FIG. 1.
However, it is difficult to apply the solder 12 of the same size and shape for each of the objective lens driving unit. If the solder 12 larger in specific gravity is deposited non-uniformly on the lens holder 2 which is displaced and operates as a movable part, the position of the center of gravity of the lens holder 2 cannot be maintained constant. Above all, if the center of gravity of the lens holder 2 is shifted in the small-sized objective lens driving unit, the objective lens 1, supported on the lens holder 2 supported in turn in a cantilevered fashion by flexibly movable supporting members, cannot be displaced correctly in mutually perpendicular biaxial directions, that is in the focusing and tracking directions. If the objective lens 1 cannot be displaced correctly in the focusing and tracking directions, the light beam radiated via the objective lens 1 on the optical recording medium cannot be converged on the signal recording area, while the light beam cannot correctly trace the recording track of the optical recording medium, as a result of which the information signals cannot be correctly recorded on or reproduced from the optical recording medium.
If, due to use of the solder 12, the position of the center of gravity of the lens holder 2 holding the objective lens 2 cannot be managed to be constant, the point of resonance of the objective lens 1 displaced by the control current supplied to the driving coils 6, 7 ceases to be constant. In such case, resonant vibration tends to be produced during driving the objective lens, with the result that it becomes impossible to produce an objective lens driving device allowing reliable displacement of the objective lens in an amount corresponding to the control current.